The present invention relates generally to the field of telecommunications, and more particularly to a method and apparatus for a start-up procedure for digital and analog modems using pulse code modulation for data transmission.
In order to achieve reliable and efficient communication over Public Switched Telephone Network (PSTN), voice-band modems go through sophisticated startup procedures. There are international standards defined by the International Telecommunications Union (ITU) that define these procedures for modems operating with different speeds. For example, ITU Recommendations V.22, V.32, V.34, and most recently V.90. These standards define the transmitter operation for modems on each end. Each individual modem vendor designs the receiver structure; however, it shall comply with the transmitter function as defined by the standard.
ITU Recommendation V.90 specification takes advantage of the fact that today""s networks including the PSTN are mostly digital and it is only thexe2x80x9clast milexe2x80x9d that still utilizes analog technology. ITU Recommendation V.90 specification specifies the mode of operation when the network topology is such that one end is digitally connected. In this scenario, one modem is connected to the PSTN via digital means, hence called the digital modem, and the other is connected via analog local loop, hence called the analog modem. In this topology, the modulation schemes in the upstream and downstream directions are different. In the downstream direction (from the digital modem to the analog modem) Pulse Code Modulation (PCM) scheme is used. In the upstream direction (from the analog modem to digital modem) the quadrature amplitude modulation (QAM) scheme as defined by the ITU Recommendation V.34 is used.
ITU Recommendation V.90 increased downstream rates nearly to the theoretical limit. However, upstream rates are still limited by the analog modulation of ITU Recommendation V.34. The achievable rates in the upstream direction can be increased if the PCM modulation is used. There are known PCM modulation schemes, as described in U.S. application Ser. No. 08/724,491, entitled, Hybrid Digital/Analog Communication Device, which is assigned to the assignee of the present invention and which is incorporated herein in its entirety by reference.
Therefore, a need exists for a method and apparatus that specifies a start-up procedure that allows the analog modem to achieve a higher connect speed for reliable data transmission using the PCM scheme in the upstream direction.
In the preferred embodiment of the present invention, a method of performing a start-up procedure for digital and analog modems over a communication channel having upstream and downstream directions is described to include the steps of sending a plurality of signals from the analog modem to the digital modem in the upstream direction over the communication channel where the digital modem receives the plurality of signals through the communication channel and calculates the characteristics of the communication channel in the upstream direction from the received plurality of signals. The method also includes the step of the digital modem determining a parameter set for the analog modem utilizing the characteristics, and the analog modem utilizing the parameter set to commence data transmission utilizing a pulse code modulation scheme in the upstream direction over the communication channel.
In a further embodiment of the present invention, an apparatus for performing a start-up procedure is described to include a first structure of a transmitter in the analog modem for sending a first plurality of signals in the upstream direction during the start-up procedure and a second structure of a transmitter in the analog modem for sending a second plurality of signals for data transmission utilizing pulse code modulation.